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Quick Answer: Thermal mass flow meters fit most nitrogen and CO2 lines in MAP machines. They measure mass flow directly in SLPM or kg/h and work from DN4 to DN25 at 1 to 10 bar. One meter can handle both gases if you select a model with multi-gas calibration. Send us your gas mix, pressure, pipe size, and flow range for a model and price.
Modified atmosphere packaging lines run small gas flows. A single tray sealer often uses 20 to 60 SLPM of nitrogen per cycle. Vertical form fill seal machines may use 10 to 30 SLPM of CO2. Gas supply pressure at the flow meter usually sits between 1 and 3 bar. Some central supply lines run at 6 to 10 bar. Tube sizes are small. Most MAP machines use 6 mm, 8 mm, or 12 mm OD tube. Some use 1/4 inch or 3/8 inch NPT.
Thermal mass flow meters are the standard choice for this duty. They measure gas mass flow directly without separate temperature and pressure transmitters. A DN15 inline thermal meter handles 0 to 100 SLPM nitrogen easily. Accuracy of ±1.0 percent of reading plus 0.5 percent of full scale is common. Response time below 0.5 seconds works well for cyclic filling. Coriolis mass flow meters are more accurate, around ±0.2 percent of reading, but cost more and weigh more. Most customers buy Coriolis for gas blending panels or for checking other meters, not for every packing line.
We do not recommend rotameters for MAP control because they have no 4-20 mA output. A rotameter cannot send flow data to the PLC that controls gas flushing.
Here is the thing. Thermal mass flow meters are gas dependent. A meter calibrated for air will not read CO2 correctly. The thermal conductivity and heat capacity of CO2 are different from nitrogen. We calibrate each meter for the target gas or a fixed gas blend. For a 70 percent nitrogen and 30 percent CO2 mix, we set the calibration curve to that composition. In practice, if your gas mix ratio is fixed, one calibration works well. If you change the mix often, select a multi-gas model that stores up to 10 gas curves.
We have seen this on customer sites many times. A frozen seafood packer in Vietnam used a needle valve on a tray sealer nitrogen line. The operator adjusted flow by feel and the waste rate was high. We supplied a DN15 inline thermal mass flow meter with 4-20 mA HART and a local display. The customer measured 30 SLPM per cycle and cut nitrogen use by 18 percent in the first month. Another customer in Saudi Arabia runs a bakery MAP line with CO2 and wanted a meter for 0 to 50 SLPM. We supplied a 1/4 inch NPT thermal mass flow meter with Modbus RTU output.
Our MAP flow meters cover 0 to 10 SLPM up to 0 to 500 SLPM full scale. Process connections include G1/4, G1/2, 1/4 NPT, 6 mm compression, 8 mm compression, and Tri-Clamp. Wetted parts are 316L stainless steel with FKM seals as standard. EPDM seals are available for food-grade dry gas. Outputs include 4-20 mA HART, RS485 Modbus RTU, and two alarm outputs. Power is 24 VDC. Standard pressure rating is 10 bar and optional high pressure is 25 bar. Display shows instantaneous flow, total flow, and gas type.
Install the meter downstream of the pressure regulator and a 5 micron filter. Keep 10 pipe diameters straight upstream and 5 downstream. Do not mount the meter directly after a solenoid valve. High frequency pulses disturb the sensor. Zero the meter after installation with no flow. For CO2 lines, avoid condensation by keeping the gas dry. Use a dew point below minus 20 degrees Celsius.
Which flow meter is best for nitrogen gas in MAP?
An inline thermal mass flow meter with 4-20 mA output is the best standard choice. It works from DN4 to DN25 and handles 0 to 500 SLPM.
Can one flow meter measure both nitrogen and CO2?
Yes. A multi-gas thermal mass flow meter stores separate calibration curves for nitrogen, CO2, air, and fixed blends. Tell us the exact mix ratio when you order.
What output signals do MAP flow meters offer?
We supply 4-20 mA HART, RS485 Modbus RTU, and two alarm outputs. Pulse output is available for totalizing.
Do you supply flow meters for 6 mm or 1/4 inch gas lines?
Yes. We offer 6 mm and 8 mm compression connections and 1/4 inch NPT. DN15 and DN25 flanges are also available.
What information do you need for a quote?
Send us the gas type, flow range in SLPM, pipe OD or DN, operating pressure in bar, and temperature. We will reply with a model, accuracy, price, and lead time.
Contact Silver Automation Instruments at Tel: +86-25-68650347, WhatsApp: +86-25-52155837, or WeChat: +86 15365082610. Send us your pressure (bar), temperature (°C), pipe size (DN), and flow range for a fast quotation. We ship from our Nanjing factory to food packers, gas blending panel builders, and distributors in Southeast Asia, the Middle East, Latin America, and Africa.
